Investigations will be continued on the qualitative and quantitative changes in cell-surface glycoproteins and surface morphological features involved in the failure of the immune response of the host to retard or halt the proliferation of tumor cells. Special attention will be devoted to studies of the possibility of masking of tumor specific transplantation antigens by large endogenous cell-surface glycoproteins in syngeneic tumor systems, which will serve as a model for autochthonous human tumors. Comparison of immunosensitive and immunoresistant sublines, in a Moloney virus-induced murine lymphoma will continue. In addition, further work will be performed on the basis for allotransplantability in a TA3 subline recently developed by an immunoselection procedure in the laboratory of Dr. George Klein in Stockholm. Several different approaches will be pursued, as a continuation of present studies. Cell-surface glycoproteins, radiolabeled or nonlabeled, will be liberated from intact cells by detergents, sonication, freeze thawing, or proteolysis. Column chromatography (gel filtration, ion exchange, and affinity), in conjunction with polyacrylamide gel electrophoresis and analytical isoelectric focusing, will be employed as isolation techniques. Antigenic activities of isolated macromolecules will be determined by the use of specific antisera. Physicochemical characterization of relevant glycoproteins isolated in sufficient quantity will be performed.